The present invention relates generally to pulse generation, and more specifically the invention pertains to a device for charging PFLs (Pulse Forming Lines) on a time scale of a few nanoseconds. Historically the most basic method for pulse generation is the discharge of a charged PFL into a load by a switch. The generation of very short pulses in the range of nanoseconds or picoseconds requires a very fast switch. High pressure gas switches which multichannel are capable of switching faster and can handle higher powers than any other type including solid state. Calculations show that switching speeds on the order of a few picoseconds are possible at several hundred kilovolts. The multichannel operation means that the switch closure consists of multichannels of conduction thus the lower switch impedance is due to the large number of parallel impedances per channel. In order to obtain multichannel operation it is necessary to "over volt" the switch, i.e. apply the voltage to the switch very rapidly. The conventional methods of applying voltage to the switch or charging the PFL is to use either a charging inductor or charging resistor. However, when the time of charging is on the order of nanoseconds charging inductors and resistors are impractical because the impedance of these components must be so low that insufficient isolation from the charging power source is provided.
The task of providing a method for rapidly charging the PFL or equivalently applying voltage to the switch is alleviated, to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 4,918,325 issued to Busby et al.;
U.S. Pat. No. 4,912,369 issued to Moran et al.;
U.S. Pat. No. 4,871,925 issued to Yamauchi et al.; and
U.S. Pat. No. 4,477,746 issued to Piltch.
The patents identified above, relate to pulse generating devices. In particular, the Busby et al. patent describes a fast rise time pulse power system. A pulse generator is electrically connected to an electrical load using a coaxial transmission line with inner and outer conductors, a polyvinyl chloride (PVC) dielectric flashover switch, a metal ring, and velvet electrical insulation between the inner and outer conductions of the transmission line. The outer conductor is directly connected between the pulse generator and the load. The inner conductor has two sections with the PVC switch fixed such that it electrically connects the two sections. The first section of the velvet covered inner conductor electrically connects the pulse generator to the PVC switch, while the second section electrically connects the PVC switch to the load. The metallic ring circumscribes the outer conductor of the transmission line near the end that is connected with the load. Such a system provides a current and voltage rise/time of subnanosecond time periods. The Moran et al. patent is directed to a triggerable, high voltage, high current, spark gap switch for use in pulse power systems. The device is triggered by introducing an arc between one electrode and a trigger pin. High repetition rates are obtained by operating the trigger at voltages below the self-breakdown voltage of the device.
The Yamauchi et al. patent relates to a high voltage pulse generating apparatus. The apparatus comprises at least one magnetic switch with a magnetic core. The core contains a soft magnetic alloy ribbon wound in a toroidal form. The alloy contains such elements as iron, copper, niobium, tantalum, molybdinum and titanium, with at least fifty percent of the alloy structure being fine crystalline particles.
The Piltch patent describes a high repetition rate switch for delivering short duration, high power electrical pulses from a power supply such that the power supply produces an electric field between the electrodes near breakdown potential. The microwave generator is connected to the microwave waveguide and produces pulses having sufficient energy to distort the electric field to cause breakdown between the rail electrodes. The rail electrodes provide a large conduction area that reduces induction effects of the switch and minimizes electrode erosion. Although these patents relate to pulse generating devices, they do not describe a device utilizing impedance matching techniques to facilitate energy flow.